Low White Blood Cell Count: Leukopenia
A low white blood cell (WBC) count is called leukopenia, and when specifically referring to low neutrophils, the term neutropenia is often used interchangeably. 1
Definition and Clinical Context
- Leukopenia is defined as an abnormal reduction of circulating white blood cells, particularly affecting the granulocytes 1
- The term is frequently used interchangeably with neutropenia in clinical practice, though technically neutropenia refers specifically to low neutrophil counts 1
- A complete blood count (CBC) typically reveals leukopenia when WBC counts fall below normal reference ranges, and this assessment should include evaluation of all cell lines (white blood cells, hemoglobin, and platelets) 2
Common Clinical Presentations
Viral Infections
- Viral infections, particularly influenza, commonly cause leukopenia while maintaining normal differential proportions 3
- In influenza A infections in children, low WBC counts (<4,000/mm³) occur in 8-27% of cases 2, 3
- H5N1 influenza demonstrates particularly severe leukopenia, with all affected children in one study showing WBC <4.0 (mean 2.44) 2, 3
- Lymphopenia (low lymphocyte count specifically) is found in 40-41% of influenza A cases 2
Immunodeficiency States
- In severe combined immunodeficiency (SCID), CBC usually reveals leukopenia, lymphopenia, or both as characteristic findings 2
- These patients present with severe age-adjusted lymphopenia and profoundly reduced T-cell populations 2
Drug-Induced and Chronic Conditions
- Medications are a leading cause of neutropenia and require comprehensive medication review 4
- Hematologic toxicities including prolonged leukopenia can occur weeks to months after certain therapies, such as CAR T-cell therapy 2
- In systemic lupus erythematosus, leukopenia occurs in 22-41.8% of patients 5
Clinical Significance
- Abnormalities in two or more cell lines (WBC, hemoglobin, platelets) warrant careful evaluation and likely consultation with a hematology specialist 2
- The major danger of neutropenia is the risk of infection, requiring identification of the underlying cause and effective antimicrobial therapy when serious systemic infection is present 1
- Isolated leukopenia with normal differentials is less concerning than leukopenia with abnormal differential counts 3